#include<stdio.h>
#include<stdlib.h>

int combination_r(int n,int r)
{
	
	if(n < r || r < 0) exit(1);
	else if(n == r || r == 0) return 1;
	else if(r == 1) return n;
	else
		return combination_r(n - 1, r) + 
			combination_r(n - 1, r - 1);
}

int combination(int n, int r)
{

}

int main(int argc,char *argv[])
{
	int i = atoi(argv[1]);
	int j = atoi(argv[2]);
	printf("%d\n", combination_r(i,j));
}

